An electric arc or arc discharge is an electrical breakdown of a gas that produces an ongoing plasma discharge, resulting from a current through normally nonconductive media such as air. An arc discharge is characterized by a lower voltage than a glow discharge, and relies on thermionic emission of electrons from the electrodes supporting the arc.
Arc faults are particularly dangerous and potentially fatal to personnel. During an arc fault in an electrical equipment enormous energy is released from the electrical housing that houses the electrical equipment and this can cause serious injuries to personnel in close vicinity of the electrical housing, including severe burns, ruptured eardrums, collapsed lungs, damaged eyesight and in some cases death. Accident reports have revealed that electricians have been injured even at distances of 3 meters or more away from the arc point. Arc faults produce large shock waves that can blow personnel off their feet and there is also the risk of being exposed to flying debris together with a possibility of temperatures at the arc point reaching as high as 20,000° C. The intense heat generated during an arcing event can vaporize the copper present in the electrical equipments and wires and the copper vapor expands to 67,000 times the volume of solid copper. Metal is blasted and splattered from the arc point. The volume of hot ionized gas produced, increases proportionally with energy. It is thus crucial to remove the source of energy as soon as possible in order to eliminate the avalanche effect of an arc flash fault.
Arc flash is common phenomenon in electrical switchboards. When an internal are happens in a switch board extreme pressure inside the panel is developed. This pressure exerts a significant force on the panel parts such as door, side panels, rear panels and roof tops often dislodging these parts and may result in an explosion. Many times working personnel become victims at workplace while operating on electrical equipments owing to this arc faults. Arc flash can cause traumatic injuries. The superheated ball of gas accompanying the flash can cause burns all over the human body and lungs. Death from these injuries is a real possibility.
Certain prior art documents discloses arc ventilation assemblies with an aim to address the above mentioned problems, including overheating and internal arcs generated in an electrical enclosure. United States patent publication 20050258141 discloses an enclosure with arc resistant features. The arc resistant feature as disclosed in US 20050258141 is provided with perforated areas and mesh openings that are aligned with the window enabling venting of hot gases generated within the electrical enclosure, but the invention disclosed in US 20050258141 is related only to pressure relief, through a flap, in case of internal arc event. It does not include any natural ventilation in normal conditions.
Similarly another prior art document, U.S. Pat. No. 7,674,996, discloses gassing insulators for arc chute assemblies being provided with wire mesh and a plurality of arc plates for reducing an arc. But the disadvantage associated with the invention disclosed in U.S. Pat. No. 7,674,996 is that the function of arc plates in this invention is to divide the arc and to increase the length of the arc. It does not provide any ventilation as such.
In addition another prior art WO/2012/118641 discloses an arc resistant transformer enclosure having arc channels. The arc resistant transformer enclosure disclosed in WO/2012/118641 has ventilation gratings, openings and a roof structure with ventilation openings and holes. But the limitation of the invention disclosed in WO/2012/118641 is that the enclosure is configured to block the path of the gases in the event of internal are whereas the subject invention filters the molten and hot particles, and also releases the gases at lower temperature and pressure.
With a view therefore to avert or to overcome the problems associated with the conventional arc ventilation units and assemblies the inventors felt the need to develop a new are deflecting and ventilating assembly that enables ventilation under normal conditions and even during an event of an arc flash. The invented are deflecting and ventilation assembly has a slotted box with a plurality of slots, an array of arc plates placed in a predefined angle within the slotted box and the slots in the box are covered with wire mesh arrangements disposed in the inner periphery of the slotted box. The invented arc deflecting and ventilation assembly is configured to vent out hot gases generated within the electrical enclosure and also filters the molted particles generated during an arc. It is also provided with arc plates which deflect the hot gases and particles downwards thereby enabling a reduction in pressure of the gases. It also facilitates controlled release of the hot gases generated during an arcing event thus the person standing in front of the switchgear is protected from injury.
In addition, the invented arc deflecting and ventilation assembly helps in reducing the pressure of gases generated during internal arc by deflecting the generated hot gases and particles and at the same time releasing the pressure out of the electrical enclosure. The invented arc deflecting and ventilation assembly is configured to be attached to electrical enclosure(s) housing electrical equipment(s) therewithin. In normal conditions the invented arc deflecting and ventilation assembly provides a path for ventilation of heat generated by the electrical component(s). The invented arc deflecting and ventilation assembly is configured to block the molten metal and hot particles escaping from the electrical enclosure during an arcing event. Thereby, the invention also enhances the personnel safety to working personnel and protects them against an arc flash.